1. Technical Field
The present invention relates to machine tools furnished with: a bed; a table on which a workpiece is carried and which is disposed on the bed; a main spindle for retaining a tool, and provided, with its axis disposed perpendicularly, to rotate freely centered on the axis; and a feed mechanism for shifting the table and the main spindle relatively to each other along three orthogonal axes.
2. Description of the Related Art
Such machine tools known to date include the example disclosed in Japanese Unexamined Patent App. Pub. 2001-87964. This machine tool primarily is made up of: a bed; a column arranged on the bed; a saddle that is supported on the front of the column and is shiftable horizontally (along the X-axis); a spindle head that is supported on the saddle and is shiftable vertically (along the Z-axis); a main spindle for retaining a tool and being supported by the spindle head so that the axis of the main spindle is perpendicular and the main spindle is rotatable about the main spindle axis; and a table on which a workpiece is carried, the table being arranged on the upper face of the bed and provided below the main spindle, provided to be shiftable along an axis (the Y-axis) that is orthogonal in the horizontal plane to the course along which the saddle shifts.
This machine tool also has a rotational drive mechanism for rotating the main spindle on the main spindle axis, an X-axis guide mechanism for guiding movement along the X-axis of the saddle, a Z-axis guide mechanism for guiding movement along the Z-axis of the spindle head, a Y-axis guide mechanism for guiding movement along the Y-axis of the table, an X-axis feed mechanism for moving the saddle on the X-axis, a Z-axis feed mechanism for moving the spindle head on the Z-axis, a Y-axis feed mechanism for moving the table on the Y-axis, a machine tool cover that is attached to the bed and surrounds the machine tool, an X-axis cover disposed in front of the cover, a Z-axis cover disposed in front of the cover, a Y-axis cover disposed above the bed, and a guide cover disposed above the bed on both sides of the table on the X-axis.
The X-axis guide mechanism comprises a first X-axis guide surface formed along the X-axis in front of the column, and a second X-axis guide surface formed behind the saddle so that the second X-axis guide surface connects with the first X-axis guide surface. The Z-axis guide mechanism comprises a first Z-axis guide surface formed along the Z-axis in front of the saddle, and a second Z-axis guide surface formed behind the spindle head so that the second Z-axis guide surface connects with the first Z-axis guide surface. The Y-axis guide mechanism comprises a first Y-axis guide surface formed along the Y-axis above the bed, and a second Y-axis guide surface formed below the table so that the second Y-axis guide surface connects with the first Y-axis guide surface.
The X-axis feed mechanism comprises an X-axis drive motor disposed to the column, an X-axis ball screw disposed along the X-axis in front of the column and axially rotated by the X-axis drive motor, and an X-axis nut that is affixed to the back of the saddle and screws onto the X-axis ball screw. The Z-axis feed mechanism comprises a Z-axis drive motor disposed to the saddle, a Z-axis ball screw disposed along the Z-axis in front of the saddle and axially rotated by the Z-axis drive motor, and a Z-axis nut that is affixed to the back of the spindle head and screws onto the Z-axis ball screw. The Y-axis feed mechanism comprises a Y-axis drive motor disposed to the bed, a Y-axis ball screw disposed along the Y-axis above the bed and axially rotated by the Y-axis drive motor, and a Y-axis nut that is affixed to the bottom of the table and screws onto the Y-axis ball screw.
The X-axis cover is a telescopic cover disposed in front of the column to allow movement of the saddle along the X-axis with both side portions and the top portion of the cover connected to the inside of the machine tool cover. The Z-axis cover is a roll-up cover disposed in front of the saddle covering the Z-axis guide mechanism and the Z-axis feed mechanism to allow movement of the spindle head along the Z-axis. The Y-axis is a telescopic cover disposed above the bed covering the Y-axis guide mechanism and Y-axis feed mechanism to allow movement of the table along the Y-axis, and is rendered so that the top of the Y-axis cover declines to both sides from the middle portion of the Y-axis cover on the X-axis. The covers prevent chips, swarf and other cutting waste and cutting fluid from flying outside the machine tool and from entering the X-axis guide mechanism and X-axis feed mechanism, the Z-axis guide mechanism and Z-axis feed mechanism, and the Y-axis guide mechanism and Y-axis feed mechanism.
The guide cover is disposed below the X-axis cover, the Z-axis cover, and the Y-axis cover, and guides waste and cutting fluid into a collection box located below drain holes appropriately formed in the bed along the X-axis on both sides of the table.
When the X-axis drive motor in this machine tool rotates the X-axis ball screw and the X-axis nut moves along the X-axis ball screw, the saddle moves along the X-axis guided by the first X-axis guide surface and the second X-axis guide surface. When the Z-axis drive motor rotates the Z-axis ball screw and the Z-axis nut moves along the Z-axis ball screw, the spindle head moves along the Z-axis guided by the first Z-axis guide surface and the second Z-axis guide surface. When the Y-axis drive motor rotates the Y-axis ball screw and the Y-axis nut moves along the Y-axis ball screw, the table moves along the Y-axis guided by the first Y-axis guide surface and the second Y-axis guide surface. The rotational drive mechanism drives the main spindle rotationally on the main spindle axis. The workpiece held on the table is thus processed by the tool held in the main spindle as the saddle, spindle head, and table move on their respective axes while the main spindle rotates on the main spindle axis.
Waste produced by machining the workpiece and cutting fluid supplied appropriately to the point of contact between the tool and the workpiece during processing are also prevented from entering the X-axis guide mechanism and X-axis feed mechanism, the Z-axis guide mechanism and Z-axis feed mechanism, and the Y-axis guide mechanism and Y-axis feed mechanism by the X-axis cover, the Z-axis cover, and the Y-axis cover, respectively, and from flying outside the machine tool by the machine tool cover.
In addition, waste and cutting fluid also fall down along the inside surface of the machine tool cover, the X-axis cover, and the Z-axis cover, and are guided downward to both sides along the X-axis by the inclined surface of the top of the Y-axis cover. The waste and cutting fluid then fall onto the top of the guide cover whereby they are guided towards the collection box and exit.
With this conventional machine tool, the Y-axis guide mechanism that guides table movement and the Y-axis feed mechanism that moves the table are located below the top of the table, and waste and cutting fluid always flow over the top of the Y-axis cover. Waste and cutting fluid can therefore enter the Y-axis guide mechanism and Y-axis feed mechanism more easily than the X-axis guide mechanism and X-axis feed mechanism or the Z-axis guide mechanism and Z-axis feed mechanism. As a result, the Y-axis cover requires frequent maintenance, or requires using a complicated and costly construction.
Another problem with the conventional technology is that the heavy saddle is supported at the front of the column and the similarly heavy spindle head is supported at the front of the saddle with the saddle and spindle head protruding to the front of the machine tool. This results in deflection or deformation of the column or saddle and thus prevents high precision machining.